The present invention relates to a radio system of the type typically represented by a portable telephone system which tunes in the transmitting channel and the receiving channel at desired frequencies. More specifically, the present invention is concerned with elimination of deterioration in radio characteristics which is due to radiation of a fundamental wave and N-th harmonic of a reference clock generated by a clock oscillation circuit built in the radio system.
In recent years, such a small-sized portable radio system as typically represented by a portable telephone system which tunes in the transmitting frequency or the receiving frequency at a desired frequency has been widely exemplified as using a microprocessor which has one chip incorporating many functions in order to realize a reduction in size and weight, a reduction in power consumption, a reduction in cost and a high-class function. When using the microprocessor, there is need for a clock oscillation means operative to generate a reference clock for synchronization. However, the clock oscillation means sometimes radiates the fundamental wave and N-th harmonic of the reference clock in the form of electromagnetic waves into a free space and when the frequencies of the electromagnetic waves coincide with, or are very close to, that of the transmitting channel or the receiving channel, the electromagnetic waves representative of the fundamental wave and N-th harmonic interfere with an electromagnetic wave representative of the transmitting or receiving channel to deteriorate radio characteristics such as a transmitting characteristic and a receiving characteristic.
Methods for elimination of a deterioration in radio characteristics have hitherto been employed including: a method of isolating all portions liable to radiate the fundamental wave and N-th harmonic of a reference clock, for example, isolating wiring conductors associated with the reference clock from the other wiring conductors by shielding the former wiring conductors with a ground line or isolating parts associated with the reference clock from radio means by enclosing these parts with a shield case made of metal; and a method of suppressing the radiation level by confirming portions liable to radiate the fundamental wave and N-th harmonic of the reference clock through, for example, trial production and adding capacitors to these portions.
JP-A-4-150230 discloses a conventional construction which can systematically achieve such elimination. In the conventional construction, there are provided as shown in FIG. 8 a receiving circuit 5100 for tuning in the receiving frequency at a desired frequency, a control circuit 6000 for performing control of the whole of a radio system, a clock oscillation circuit 1000 adapted to generate a reference clock signal 1200 for the control circuit 6000, a measuring reference oscillation circuit 1100 for generating a highly accurate oscillation frequency which serves as a reference of measurement of the oscillation frequency of the reference clock 1200, a measuring circuit 7000 for measuring the frequency of the reference clock 1200 generated by the clock oscillation circuit 1000 in relation to the reference of the oscillation frequency of the measuring reference oscillation circuit 1100, a comparative arithmetic circuit 3000 for comparing a receiving frequency 5200 tuned in by the receiving circuit 5100 with a result of measurement by the measuring circuit 7000, and a frequency switching circuit 4000 for switching the oscillation frequency of the reference clock 1200 generated by the clock oscillation circuit 1000 on the basis of a result of comparison by the comparative arithmetic circuit 3000.
Next, the operation of the aforementioned prior art example will be described. In the prior art example, when the radio system is started, the control circuit 6000 begins to initialize the individual circuits. At that time, the frequency switching circuit 4000 delivers a switching signal 4001 for setting the oscillation frequency of the reference clock 1200 to be generated by the clock oscillation circuit 1000 to a first oscillation frequency. The clock oscillation circuit 1000 applied with the switching signal 4001 sets the oscillation frequency of the reference clock 1200 to the first oscillation frequency. The measuring circuit 7000 then begins to accurately measure the oscillation frequency of the reference clock 1200 to be generated by the clock oscillation circuit 1000 in relation to the reference of the oscillation frequency of the measuring reference oscillation circuit 1100. When the initialization ends, the control circuit 6000 controls the receiving circuit 5100 to cause it to sequentially scan receiving frequencies, tune in a desired frequency and begin to receive the desired frequency. At that time, the comparative arithmetic circuit 3000 compares the receiving frequency tuned in by the receiving circuit 5100, the oscillation frequency of the reference clock 1200 measured by the measuring circuit 7000, whereby when radiation of the fundamental wave and N-th harmonic of the reference clock 1200 is decided to be of frequencies which interfere with the receiving frequency tuned in by the receiving circuit 5100, the frequency switching circuit 4000 delivers a switching signal 4001 for setting the oscillation frequency of the reference clock 1200 to be generated by the clock oscillation circuit 1000 to a second oscillation frequency. The clock oscillation circuit 1000 applied with the switching signal 4001 sets the oscillation frequency of the reference clock 1200 to the second oscillation frequency. The comparative arithmetic circuit 3000 then compares the receiving frequency tuned in by the receiving circuit 5100 with the oscillation frequency of the reference clock 1200 measured by the measuring circuit 7000, whereby when radiation of the fundamental wave and N-th harmonic of the reference clock 1200 is decided to be of frequencies which do not interfere with the receiving frequency tuned in by the receiving circuit 5100, the frequency switching circuit 4000 delivers a switching signal 4001 for setting the oscillation frequency of the reference clock 1200 to be generated by the clock oscillation circuit 1000 to the first oscillation frequency. The clock oscillation circuit 1000 applied with the switching signal 4001 sets the oscillation frequency of the reference clock 1200 to the first oscillation frequency.
Thus, by alternately switching the oscillation frequency of the reference clock 1200 to be generated by the clock oscillation circuit 1000 to the first and second frequencies in accordance with a receiving frequency tuned in by the receiving circuit 5100, radiation of electromagnetic waves of the fundamental wave and N-th harmonic of the reference clock generated by the clock oscillation circuit 1000 can be prevented from interfering with that receiving frequency tuned in by the receiving circuit 5100, thereby eliminating a deterioration in radio characteristics.
However, in the conventional radio system described as above, a shield case made of metal, for example, is needed which prevents the influence of electromagnetic waves of the fundamental wave and N-th harmonic of the reference clock signal radiated from portions associated with the clock oscillation circuit, in order to eliminate a deterioration in radio characteristics, raising a problem that a reduction in size and weight is difficult to achieve, and when suppressing the radiation level of electromagnetic waves of the fundamental wave and N-th harmonic of the reference clock signal by adding capacitors, it is very difficult to predict, during the design procedure, portions to which capacitors are added and hence radiating portions must be confirmed once by using a trial product of the radio system, raising a problem that the period for design and development of the radio system is considerably prolonged. Further, in the method for suppressing the radiation level, there is a possibility that the elimination effect cannot be obtained with some products depending on irregularity in parts and production, raising a problem that the yield during production is degraded.
Further, in JP-A-4-150230 additionally provided with the measuring reference oscillation circuit 1100, replacement of this circuit with software means inside the microprocessor is difficult to achieve and therefore, a separate oscillation circuit must be provided, increasing the circuit scale. In addition, radiation of the fundamental wave and N-harmonic of the oscillation frequency of the measuring reference oscillation circuit 1100 also deteriorates radio characteristics, raising a problem that the comparative arithmetic processing by the comparative arithmetic circuit 3000 must simultaneously cope with this type of deterioration in radio characteristics and so becomes complicated.
The present invention contemplates elimination of the aforementioned problems and it is an object of the invention to provide a radio system in which circuits and construction of the radio system can be simplified by reducing weight and size so as to decrease the period for development and design and to improve productivity.
To solve the above problems, a radio system according to the present invention comprises radio means for tuning in a desired frequency, control means for performing control of the whole of the radio system, clock oscillation means operative to generate a reference clock for the control means, memory means operative to store conditions for switching the oscillation frequency of the reference clock to be generated by the clock oscillation means, comparative arithmetic means for comparing a frequency tuned in by the radio means with the conditions stored in the memory means, and frequency switching means for switching the oscillation frequency of the reference clock to be generated by the clock oscillation means, on the basis of a result of comparison by the comparative arithmetic means, wherein the oscillation frequency of the reference clock to be generated by the clock oscillation means is switched by controlling the frequency switching means on the basis of a result of comparison by the comparative arithmetic means.
Also, to solve the above problems, a radio system according to the present invention comprises radio means for tuning in a desired frequency, control means for performing control of the whole of the radio system, clock oscillation means operative to generate a reference clock for the control means, memory means for storing frequencies to be tuned in by the radio means and conditions for switching the oscillation frequency of the reference clock to be generated by the clock oscillation means, and frequency switching means for switching the oscillation frequency of the reference clock to be generated by the clock oscillation means on the basis of the conditions stored in the memory means, wherein the radio means tunes in a frequency stored in the memory means and the oscillation frequency of the reference clock to be generated by the clock oscillation means is switched by controlling the frequency switching means on the basis of a condition stored in the memory means and corresponding to the tuned-in frequency.
Accordingly, with the construction of the present invention described above, the frequency switching means is controlled on the basis of a frequency tuned in by the radio means and the memory contents stored in the memory means to switch the oscillation frequency of the reference clock to be generated by the clock oscillation means, whereby radiation of electromagnetic waves of fundamental wave and N-th harmonic of the reference clock of the clock oscillation means can be prevented from interfering with a frequency being tuned in and a deterioration in radio characteristics can be eliminated steadily.